The purpose of this research is to elucidate some of the factors which control the shedding of the rod outer segment discs and their subsequent phagocytosis by the pigment epithelium. It is hoped that better knowledge about these processes may lead to a better understanding of degenerative diseases of the retina, such as retinitis pigmentosa. Intact animals will be subjected to altered lighting regimens, and the shedding rhythm will be assessed after varying times in the new environment. Once understood, the shift in shedding will be used to assess the importance of various factors in the shedding rhythm by severing neural pathways, or by interfering with these pathways by the introduction of appropriate biochemical agents and determining whether the animal then responds to altered lighting in a normal fashion. Other tests will use histochemical and autoradiographic probes to attempt to map biochemical changes thought to be involved with the shedding process. Rats with inherited retinal dystrophy will be compared to normal rats to determine which of these factors are altered in the dystrophic animals.